Some of pharmaceutical products and specimens handled in medical facilities such as hospitals, and some of foods and the like available in supermarkets and the like need to be kept cold or warm within a certain temperature range during transportation so that their qualities are maintained.
As a method of keeping such articles (e.g., pharmaceutical products, specimens, foods, and the like) cold or warm, there has conventionally been known a method in which (i) a heat storage material, which has been melted or solidified in advance, is placed in a transport container having a thermal insulation property and (ii) latent heat of the heat storage material is utilized so that an article placed in the transport container is kept cold or warm. In order that the temperature of an article to be kept cold or warm can be maintained within a certain temperature range for a long period of time, it is preferable to use a heat storage material that (i) has a melting point or a solidifying point within the certain temperature range and (ii) has a large quantity of latent heat.
A heat storage material containing water as its main component has commonly been used as an inexpensive and safe heat storage material having a large quantity of latent heat. Water has a melting point at around 0° C. Therefore, in a case where the temperature of an article needs to be controlled at a temperature of not higher than 0° C., (i) a solidifying point depressant is added to the water so that the melting point is adjusted to be not higher than 0° C., and (ii) a resultant mixture of the water and the solidifying point depressant is used as a heat storage material composition. However, in a case where a control temperature (i.e., a temperature at which the temperature of an article needs to be controlled) is above 0° C., it is difficult to use a heat storage material composition, containing water as its main component, to control the temperature of an article at its desired control temperature. Specific examples of an article whose control temperature is above 0° C. include blood, blood plasma, specimens, and pharmaceutical products. Generally, specimens are preferably kept at a control temperature of 4° C. to 6° C. during transportation, and pharmaceutical products are preferably kept at a control temperature of 2° C. to 8° C. during transportation.
As above, there exist many articles that need to be controlled at a temperature above 0° C., and therefore a large number of studies have been made in regard to a heat storage material composition that can be used to store or transport such articles. For example, there have been many cases of studies made on a composition containing, as its main component, sodium sulfate 10-hydrate which is one of inorganic hydrated salts having a large quantity of latent heat. Specifically, Patent Literatures 1 to 6 each disclose an example of a heat storage material composition which contains sodium sulfate 10-hydrate as its essential component and which, optionally, further contains a melting point adjuster containing, for example, an ammonium salt, a halogenated salt, and/or another inorganic salt(s).